Couplings for high pressure lines, particularly those intended for use subsea, are customarily self-sealing, normally comprising a female coupler or receiver and a male coupler or probe insertable in the receiver. The couplers include mutually engageable means, normally spring loaded poppet valves, which engage when the couplings are mated so the high pressure fluid can flow from one coupler to the other coupler, and seal the ends of the couplers and the lines connected to them when the couplers are disengaged. It is necessary to provide at least one seal between the couplers and normally at least two seals between them in order to prevent egress of hydraulic working fluid from the coupling and, particularly for use subsea, to inhibit ingress of seawater into the interior of the coupling. Such seals are required to be durable and reliable because the couplings are usually required to remain operational for very long periods of time.
Various different forms of seal have been proposed for such couplings. Such forms include crush seals between axially confronting parts of the couplers and more recently pressure-responsive resilient metal seals, usually with a C-section. Examples of the latter form of seal are provided by British Patents Nos. 2183310 and 2201212, U.S. Pat. Nos. 4834139 and 4768538.
Some of the couplings described in the foregoing Patents and also various other forms of coupling have employed a elastomeric seal, usually an O-ring seals, usually as a second seal auxiliary to a metallic crush seal or radial pressure responsive metal seal. Elastomeric seals and particularly elastomeric O-rings are attractive for reasons of reliability and simplicity of design, but have the disadvantage in male/female self-sealing subsea couplings that such seals have a tendency to be displaced when the couplers are parted. On separation of the male and female couplers, there is normally a phase in which there is a tendency for the creation of a vacuum in the space between the couplers and the consequent rapid inrush of external fluid (such as seawater) into the space can dislodge the seal from its location, which is usually an annular recess inside the bore of the female coupler.